The present invention relates to tubular type heat exchangers wherein heat is transferred from a hot fluid flowing over the tubes to a cooler fluid to be heated flowing through the tubes and, more particularly, to such a tubular heat exchanger wherein a turbulator is disposed within the tube to increase convective heat transfer to the fluid flowing through the tube by creating turbulence which reduces the formation of boundary layers along the inside tube wall.
Recuperative heat exhangers of the tubular type are well known in the art. Such recuperative heat exchangers typically comprising a housing defining a flow conduit through which the hot fluid, typically flue gas from a boiler, passes. A plurality of heat exchange tubes are disposed to extend through the housing tranversely to the flow of the hot fluid therethrough. The cooler fluid, typically combustion air, to be heated is passed through the interior of the tubes in indirect heat exchange relationship with the hot fluid flowing over the outside of the heat exchange tubes. As the hot fluid flows over the outside of the heat exchange tubes, the hot fluid is cooled by transferring some of its heat to the tube by convection. The heat absorbed by the tube walls is in turn transferred by convection to the cooler fluid flowing through the interior of the tubes thereby heating the cooler fluid.
It is known in the prior art to provide turbulator means within the interior of the heat exchange tubes to create a turbulent flow through the interior of the heat exchange tubes thereby breaking down the formation of boundary layers along the inside tube wall which would hinder convective heat transfer. A typical type of turbulator, as shown in U.S. Pat. No. 1,770,280, comprises a relatively thin, elongated, twisted ribbon of material having a width slightly less than the inside diameter of the heat exchange tube. As the cooler fluid to be heated passes through the heat exchange tube, it must follow a spiral path about this twisted ribbon of material. Because of this, turbulent flow is established within the heat exchange tube and boundary layer formation along the inside wall is greatly reduced.
Turbulent heat exchangers with turbulators are typically employed to transfer heat from a flue gas having a temperature in the range of 500 F. to 1500 F. to a stream of ambient air to be heated for combustion. In this range of temperatures, convection heat transfer is responsible for most of the heat exchange. However, radiative heat exchange is significant with the hot fluid in the temperature range of about 1800 F. or higher, and is present to a lesser extent at temperatures as low as 1200 F. Typical prior art tubular recuperators of the type described above are not satisfactorily equipped to take advantage of radiative heat transfer from these hot fluids.
Accordingly, it is therefore an object of the present invention to enhance the performance of such tubular heat exchangers for use in transferring heat from a hot fluid to a cooler fluid by enhancing radiative heat transfer from the hot fluid to the cooler fluid.
A further object of the present invention is to enhance radiative heat transfer from the hot fluid to the cooler fluid by augmenting radiative heat transfer from the heat exchange tube to the turbulator disposed therein whereby the turbulator receives a portion of the heat transferred to the heat exchange tubes from the hot fluid and in turn transfers this heat by convection to the cooler fluid flowing through the interior of the heat exchange tubes and over the turbulator disposed therein.